This invention relates to a data processing and memory system.
In particular, the invention is concerned with a demand-paged system comprising a first memory, such as a video RAM, and at least one second memory, such as a disk drive, each for storing an array of data-elements, such as pixel data, and a processing means which is operable to modify the data-elements in the first memory and to transfer data-elements page-by-page between the memories.
In a demand-paged system of this type, it might be considered appropriate that when a new image is generated, the or each page of the image is allocated a respective page of locations in one of the memories, and the initial background colour of the image is written to every location in those pages. In the preferred embodiment of the invention described later, the maximum size of an image is 2.sup.32 pixels (or 4 Gigapixels) each of 32-bits, and it will be appreciated that writing the background colour to each pixel location would take an inordinate amount of processing time.
The present invention aims to mitigate the above problem, and in accordance with the invention the processing means is operable to store, when generating the or each new page in a new image, one or more data-elements less in number than the number of data elements in a page (and preferably one), and then when each new page is to be accessed the stored data-element(s) for the new page is repeated to form the data-elements of the page. Thus, in the preferred embodiment, when a new page of a new image is generated, the background colour of the image is stored for the new page, and the full page-worth of data-elements is not generated until the page is required to be accessed by the processing means. Thus, the initial set-up time for the new image is reduced substantially. A further advantage is that in many applications not all of the pages of an image will be modified, but will remain as the background colour. For such pages, the full page-worth of data-elements need never be generated.